An EV battery pack typically includes several battery modules, each comprised out of several batteries (e.g., several single cell batteries), that are packed into a hardened package. The specification of the battery pack is determined by the car manufacturer and takes into consideration the extreme needs of the engine and the expected environmental conditions. Thus the specification usually calls for extra battery modules and/or for extra material, such as electrolyte, to be added to the cells to compensate for production faults and degradation of the batteries over time. Additionally, EV battery packs have a fixed current and voltage output.
Because electric engines need high current in order to produce high torque and high voltage to produce high speed, the engine's demands from the battery pack change over time as the car goes from a state of high acceleration to a high speed state.